The present technology relates to vision systems, and more specifically, to a vision system with a swappable camera.
In a vision system with a swappable camera, in many situations, it is important that the camera remains aligned at a target when the camera is swapped for a replacement camera. In other words, the optical axis of a camera relative to the mounting points ought to be pointed precisely and repeatedly from camera to camera. It is known that the camera housing for a swappable camera can be reproducibly oriented within a vision system by way of a mounting system (i.e., the camera housing can be reproducibly pointed in the same direction upon swapping). It is also known that the lenses of a camera can be reproducibly oriented relative to the camera housing by way of the design of the camera housing even at a high manufacturing rate (i.e., the lenses can be positioned relative to the camera housing such that the image projection is reproducibly located within the camera housing). However, these steps are not sufficient unless one can also reproducibly align an image sensor chip or sensor array therein relative to the camera housing and lenses, and this needs to be done at a reasonable cost when manufacturing at a high rate of speed and in volume. Presently, there are several strategies for overcoming this difficulty in alignment, but each of the existing strategies has significant shortcomings.
One option known in the art is careful physical alignment during manufacture. At the time of manufacturing, a user can physically align a sensor assembly within a camera housing to compensate for any stack-up tolerance from the sensor chip, or other misalignments. However, this careful physical alignment slows the manufacturing process, and therefore increases the cost associated with manufacturing.
A second option known in the art is to mount the camera to an external correction stage and manually compensate for any tolerance variations in the camera. This requires additional time for the user during the camera swapping process. Also, the external correction stage is an additional expense to the overall system.
A third option known in the art is to accept the inherent variations from a high-speed manufacturing process and design a system having a camera field-of-view that is large enough to allow for sensor tolerances and a system that functions based on finding a reference object and fixturing tools to the location of the object. However, in systems where reference objects are not available, this sort of a system is not capable of proper alignment.
Finally, a fourth option known in the art is to do application-level calibration and do all computations using “real-world” coordinates. See, for example, Tsai, R. Y., “A Versatile Camera Calibration Technique for High-Accuracy 3D Machine Vision Metrology Using Off-the-Shelf TV Cameras and Lenses”, IEEE Journal of Robotics and Automation, Vol. RA-3, No. 4, August 1987. However, this option has significant computational demands that increase the cost and time to set up.
Therefore, what is needed is a vision system with a swappable camera where the swappable camera can be manufactured at a high rate of speed and at low cost, thus enabling use of cameras that are not perfectly aligned.